Heat exchangers typically include a centralized plurality of heat exchanger tubes or passageways connected at each respective end thereof to one of an inlet tank and an outlet tank. The inlet tank and the outlet tank each typically include one substantially planar surface that acts as a header for receiving the heat exchanger tubes therein. The header of each of the tanks is then coupled to a casing of the tanks that aids in distributing or collecting a fluid flowing through the heat exchanger tubes. The casing of each of the inlet tank and the outlet tank often includes a conduit connected to a portion of the casing having an expanding wall geometry used to cover a periphery of the header, wherein the header and the casing cooperate to define a hollow interior chamber through which the fluid passes during use of the heat exchanger.
Internal pressures experienced within either of the inlet tank or the outlet tank may cause a bending moment to form within each of the casings, thereby dividing the casing into portions undergoing compressive stresses and portions undergoing tensile stresses. FIGS. 1 and 2 illustrate a casing 1 according to the prior art. The casing 1 includes a pair of neutral stress lines A extending along a length thereof. The neutral stress lines A may be formed symmetrically on each side of the casing 1, hence only one of the neutral stress lines A is pictured in FIG. 1. Each of the neutral stress lines A corresponds to a portion of the casing 1 wherein stresses caused by such a bending moment are minimized due to a transition from the compressive stresses to the tensile stresses experienced within the casing 1. The portion of the casing 1 disposed between the two neutral stress lines A and corresponding to a spine of the casing 1 undergoes compressive stresses while each portion of the casing 1 formed beneath the neutral stress lines A undergoes tensile stresses.
The prior art casing 1 further includes a plurality of ribs 2 formed on an exterior surface thereof to further strengthen the casing 1 to avoid deformation. The casing 1 illustrated in FIGS. 1 and 2 includes an outwardly extending foot 3 formed around a periphery thereof having a plurality of substantially semi-circular crimp joints 4 protruding therefrom. The crimp joints 4 are included on the foot 3 of the casing 1 for coupling a ribbon crimp strip 5 of an associated header (not shown) to the casing 1. As shown in FIG. 2, the ribbon crimp strip 5 is a corrugated strip of material including recessed portions 6 configured to be disposed on the foot 3 of the casing 1 and projecting portions 7 configured to extend around and receive the substantially semi-circular crimp joints 4. Accordingly, the header may be coupled to the casing 1 by securing the ribbon crimp strip 5 of the header to the foot 3 of the casing 1 about a perimeter thereof.
Each of the ribs 2 extends from one of the semi-circular crimp joints 4 to an oppositely arranged one of the crimp joints 4, causing each of the ribs 2 to be substantially arcuate in shape. The ribs 2 project away from an exterior surface of the casing with a substantially rectangular cross-section that extends about the entire arcuate shape of each of the ribs 2, as best shown in FIG. 2. The rectangular cross-section of each of the ribs 2 creates several sharp edges and sudden transitions from one portion of the exterior surface of the casing 1 to an adjoining portion.
The ribs 2 illustrated in FIG. 1 are spaced apart from each other equally to cause the ribs 2 to have a constant frequency of occurrence in the longitudinal direction of the casing 1. Such an arrangement ensures that the casing 1 is reinforced along any and all potential problem areas. In contrast, FIG. 3 illustrates a casing 1′ that is identical to the casing 1 illustrated in FIGS. 1 and 2 except the casing 1′ includes the ribs 2 formed on an exterior surface thereof only along those portions of the casing 1′ undergoing the greatest amount of internal stresses. Accordingly, the casing 1′ of FIG. 3 reduces the amount of material used to form the casing 1′ while also addressing the issue of localized stresses formed therein.
Unfortunately, one issue associated with the use of the ribs 2 illustrated in FIGS. 1-3 is the ribs 2 are not formed on the exterior surface of the casings 1, 1′ in a manner that accounts for the variation of the stress encountered along different portions of each of the ribs 2 as they extend in an arcuate shape. Specifically, the ribs 2 tend to extend around an entirety of the exterior surface of the casing 1 wherein portions of the casing 1 experiencing a relatively low stress such as regions adjacent each of the neutral stress lines A are unnecessarily reinforced. Thus, excess material is used in forming each of the casings 1, 1′, thereby adding weight, cost, and complexity to the formation of the casings 1, 1′. Furthermore, if additional reinforcing is desired beyond that illustrated in FIGS. 1-3, each of the ribs 2 used to reinforce the casings 1, 1′ may need an enlarged cross-sectional shape to account for the additional degree of reinforcement. Such an increase in the size of the ribs 2 may undesirably increase a package size of the casings 1, 1′, which in turn may necessitate a rearrangement or modification of other components adjacent the casings 1, 1′ when one of the casings 1, 1′ is installed within a vehicle or other apparatus where a packaging space is limited.
One other issue encountered by the use of the ribs 2 shown in FIGS. 1-3 is the substantially rectangular cross-sectional shape of each of the ribs 2 may lead to local stress raisers within the casings 1, 1′ caused by the sudden change in geometry from the exterior surface of each of the casings 1, 1′ to the perpendicularly projecting ribs 2 formed thereon. The rectangular cross-sectional shape of the ribs 2 may also cause a molding operation used to form the casings 1, 1′ to take longer than would a molding of a casing having a more continuous exterior profile, as the molding material typically takes longer to reach the sharp edges and corners formed between such features during the molding process.
One other prior art solution includes the addition of cross-webbing extending between adjacent ones of the ribs to further reinforce and strengthen the casing at selected regions, and especially adjacent the foot of the casing. The cross-webbing may include one or more raised portions of the exterior surface of the casing similar to the ribs and extending in a direction perpendicular to the ribs. However, the addition of cross-webbing adds additional weight to the casing while also significantly increasing the complexity of the manufacturing process used to form the casing.
It would therefore be desirable to produce a casing for a heat exchanger that reinforces only selected regions of the casing while also minimizing a quantity of material needed to manufacture the casing.